How can you speed up your laptops performance on startup?

I got my acer aspire from Harvey Norman back in October, when I first got it, it was very fast and ran so smoothly, I would open it up it would turn on in literally 2 seconds and I could open the internet browser up straight away and dash straight into browsing or whatever work I was doing. Now it takes ages for Windows to open up, and it keeps loading, and it's a good 15 minutes before everything starts running smoothly, even typing this question is painstakingly slow, I'm typing on the keyboard and there is a delay before the letters show up on screen? I have bullguard anti virus and run regular scans to clear off any viruses and/or cookies, whatever that is lol! :D